1. Field of the Invention
The present invention relates to a magnesium-based amphoteric buffer that safely adsorbs and treats many kinds of spills and vapors and is produced from an optimal mixture of magnesium oxide (magnesia) or magnesium hydroxide, sulfuric acid and water to yield a product that neutralizes both acids and bases.
2. Description of the Prior Art
Many techniques in the prior art deal with liquid spills. Some rely on sorbent (i.e., absorbent or adsorbent) materials to soak up liquid spills. If the absorbed material is acidic or basic (alkaline), the spill may require neutralization. Neutralization frequently relies on inefficient chemical reactions or on reagents capable of neutralizing only an acid or a base but not both.
Prior art teaches the use of blends of chemicals that overcome this limitation. For example, one such blend comprises magnesia, such as MAGOX(copyright) 93 LR 325, and Epsom salts (MgSO4.7H2O) in a ⅓ to ⅔ weight ratio, respectively. This blend is sold under the tradename xe2x80x9cpH 9xe2x80x9d by Terra Environmental and is capable of neutralizing both acids and bases. Magnesia reacts with acids and Epsom salt reacts with alkalis. A serious drawback of this composition is a tendency to form a hard xe2x80x9ccakexe2x80x9d under certain storage conditions. For example, heat can dehydrate Epsom salt and hydrate magnesia into a hard cake. Alternatively, magnesium oxysulfate can form and create salt bridges between oxide particles.
A need persists for a non-caking amphoteric buffer that combines good neutralizing capacity with good storage properties, especially under warm or humid conditions.
The present invention relates to a method of using a magnesium-based amphoteric buffer that safely absorbs and treats many types of spills or vapors, and is resistant to hardening and caking while being stored. The amphoteric buffer of the present invention is described as an efficient and effective neutralizer of both acids and bases.
In a broad aspect, the amphoteric buffer comprises a basic magnesium compound and partially hydrated magnesium sulfate. Basic magnesium compound can neutralize acidic spills, and partially hydrated magnesium sulfate can neutralize alkali spills. Their combination can thereby render both acidic and alkali spills reasonably safe to handle.
One aspect teaches an amphoteric base formed by mixing sulfuric acid with an excess stoichiometry of magnesium hydroxide and/or magnesium hydroxide. Water may be added as needed to adjust the hydration of the resultant magnesium sulfate. Importantly, hydrated magnesium sulfate should comprise little or no Epsom salt, and preferably will comprise magnesium sulfate monohydrate. Conveniently, one or more pH indicators may be added to the buffer.
A magnesium-based amphoteric buffer can be produced by the direct addition, with mixing, of an appropriate quantity of sulfuric acid and water, to magnesium oxide and/or magnesium hydroxide. This produces, in-situ, a mixture of magnesium sulfate in various states of hydration, and magnesium oxide and/or hydroxide depending on whether magnesium oxide or magnesium hydroxide is used as an ingredient. For convenience, magnesium oxide and magnesium hydroxide shall hereafter be referred to as either xe2x80x9cbasic magnesium compoundxe2x80x9d or xe2x80x9cmagnesia.xe2x80x9d
Sulfuric acid is added directly to magnesia during manufacture of the material. The use of standard, readily available, commercial strength sulfuric acid permits economical and cost effective production of the material. Water may be added in a separate addition to adjust the hydration of the final product. Importantly, magnesium sulfate should be substantially present in non-hydrated form or in a hydrated form other than Epsom salt, that is, the fully hydrated form of magnesium oxide having seven water molecules. The amphoteric buffer of the present invention provides good absorbency, neutralizes both acids and bases, stores without caking, and is economically manufactured.
The direct addition of sulfuric acid to magnesia, in the manner described herein, avoids intermediate compounds and additional steps as described in the prior art. The fundamental reaction producing partially hydrated magnesium sulfated is as follows:
MgO (and/or MgOH)+H2SO4+xH2O=MgSO4.yH2Oxe2x80x83xe2x80x83(1)
wherein x and y are integers greater than zero. Preferable, y is 1-5 and, more preferably, y is 1-3.
Magnesia should be used in excess of a stoichiometric amount so that a mixture of partially hydrated magnesium sulfate and magnesia results. The number of waters of hydration (y) combined with magnesium sulfate is dependent upon the quantity of water added as a reactant. Not all of the reactant water (x) become associate with the magnesium sulfate. For example, some water is lost due to steam generation during the reaction and a minor amount can hydrate magnesium oxide to magnesium hydroxide.
This mixture is amphoteric because it is capable of neutralizing both acids and alkalis. Depending on the type of spill, neutralization means either increasing or decreasing the spill""s pH to a range safe for handling, usually from about 4-10. Magnesia can neutralize acids with the reaction products being the magnesium salt of the acid and water. Reaction (2) is representative of a reaction occurring during a spill clean-up of hydrochloric acid.
MgO (and/or MgOH)+2HCl=MgCl2+H2Oxe2x80x83xe2x80x83(2)
Magnesium sulfate is capable of reacting with alkaline solutions, which have a pH above the precipitation point of magnesium ion, for example, sodium hydroxide, lime slurries and ammonia solutions. This reaction results in the removal of hydroxyl ion from solution by precipitation of magnesium hydroxide. Reaction (3) is representative of a reaction occurring in a spill of caustic soda.
MgSO4+2NaOH=Mg(OH)2+2NaSO4xe2x80x83xe2x80x83(3)
This buffering effect produces a neutralized material with a resultant pH from about 9-10, which is significantly less dangerous than that of the un-neutralized acid or alkali.
Incorporating at least one pH indicator into the buffer gives a visual check as to whether the spill has been neutralized to a safe pH level. The indicator serves to improve the effective use of the material for application on corrosive materials without complicating the training required for proper use. Convenient pH indicators include methyl orange, ethyl orange, azoviolet, methyl red, bromothymol blue and thymol blue. Some indicators can be used in combination, for example, (a) methyl orange and azoviolet, (b) ethyl orange and azoviolet, and (c) methyl red, bromothymol blue and thymol blue. Other indicators and combinations may be used, and the invention is not limited to those described. Any indicator or combination that visually shows pH changes is acceptable. The amount of indicator(s) in the product can vary depending on the desired color intensity.
A key feature of the invention is ensuring that magnesium sulfate is hydrated in the correct range. Excessive hydration tends cause caking in the product upon storage at elevated temperatures. Correct hydration will enable the product to remain free-flowing indefinitely under proper storage conditions. Correct hydration also lessens heat formation during spill clean-up of acidic solutions. To ensure correct hydration, water is preferably added during production after the addition of sulfuric acid. The method of the present invention, as described above, makes it possible to control manufacture of the final material in an economical and efficient manner. Compositions, which are hydrated at less than equilibrium amounts, will tend to generate heat when mixed with aqueous solutions, for example, during spill clean-up. Such exothermic reactions can be undesirable. On the other hand, compositions, which are hydrated at or near equilibrium amounts, that is, Epsom salt, tend to harden under certain ambient environmental or clean-up conditions. Hardening is often undesirable. The specific composition range of the present invention reduces undesirable exothermic or hardening scenerios, which could be found during storage or application. The method employed during manufacture increases control of the type and range of compositions produced while reducing the cost of production.
Hydrated magnesium sulfate of the present invention can be formed from reactants comprising by weight percent: sulfuric acid (98% concentration) 15-35%, preferably 20-30%, most preferably about 25%; magnesia 55-75%, preferably 60-70%, most preferably about 65%; and water 5-20%, preferably 5-15%, most preferably about 10%. The process aims to produce a product that is approximately two-thirds magnesium oxide and one-third MgSO4.xH2O. The percentages may be adjusted in a known manner such as using different dilutions of reagents.
The preferred method of production is the combination of magnesia with sulfuric acid and water in a suitable mixer, such as Hobart or screw mixers. The material can be processed batchwise or continuously. The preferred purity of magnesia is between 60-100%. Sulfuric acid of 98% concentration is preferred, but other concentrations of sulfuric acid can also be used, preferably from 50-98%. The sulfuric acid is preferably added in a controlled manner to reduce heat generation and with sufficient mixing to ensure rapid dispersal of the acid in the body of the mixture. Water can be added to the mixture after acid addition. After water addition, a pH indicator can be incorporated into the mixture.
Other additives may be added to produce differing neutralization functions of the final material. All such additions should occur before sizing of the magnesium oxide product. Sizing can be accomplished by any known apparatus, such as a ball mill. The size of the resultant particles should be large enough to avoid dusting, but small enough to permit rapid reaction with the spill.